09 Ddcauado.net Cg Session04

7/30/2019 09 Ddcauado.net Cg Session04

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Instructor InputsSess

ion4


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NIIT Instructor Inputs 4.3

This session covers Chapter 3.

To understand the concepts covered in the session, the students should be aware of the

following concepts/skills:

Implementing data binding to display values on the controls of a Windows form Filtering data to display the selected records Understanding the ADO.NET architecture Managing connections in ADO.NET Working knowledge of SQL Server 2005 Understanding the application of command objects Working knowledge of the ADO.NET connected environment

This session discusses the connected and disconnected environment in ADO.NET. In

addition, it discusses the command objects used to access data from a data source in a

connected ADO.NET environment. To enable students to better understand the concepts,encourage them to provide their own examples, wherever required. Use the animated

slides, wherever provided, to conduct the session effectively.

Session Overview

Prerequisite Knowledge for the Session

Tips for Handling the Session


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4.4 Instructor Inputs NIIT

Slide 1

Slide 1 of 28Ver. 1.0

Developing Data-Centric Applications Using ADO.NET

Session 4

In this session, you will learn to:

Identify the connected and disconnected environment in

ADO.NET

Working in a connected environment

Objectives

Start the session by sharing the session objectives with the students.

Slide 2



Session 4

A connected environment is one in which a user or an

application is constantly connected to a data source.

A connected environment provides the following

advantages:

Data concurrency issues are easier to control.

Data is current and updated.

A connected environment has the following disadvantages:

A constant network connection may, sometimes, lead to

network traffic logging.

Scalability and performance issues in applications.

Let us now discuss the disconnected environment.

Introducing Connected and Disconnected Environment

Initiate a discussion in the class by asking students what happens when multiple users

simultaneously access a data-centric application to retrieve and update data. Lead the

discussion towards explaining a connected environment. In addition, state its advantagesand disadvantages.


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Slide 3



Session4

In a disconnected environment is one in which a user or an

application is not directly connected to a data source.

A disconnected environment provides the following

advantages:

Allows multiple applications to simultaneously interact with the

data source.

Improves the scalability and performance of applications.

A disconnected environment has the following

disadvantages:

Data is not always up to date as no proper connection is

established with the data source.

Data concurrency issues can occur when multiple users are

updating the data to the data source.

Introducing Connected and Disconnected Environment (Contd.)

Move the discussion towards a disconnected environment. Ask the students whether it is

possible for users to perform modifications on the data without being directly connected

to a data source.

Lead the discussion towards explaining disconnected environment. In addition, state its

advantages and disadvantages, with the help of an example given in the SG.

Slide 4



Session4

The following figure shows the connected and disconnected

environment in ADO.NET.

Introducing Connected and Disconnected Environment (Contd.)

XML Data Source


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Use the animated slide to explain the ADO.NET disconnected and connected classes.

Slide 5



Session 4

A Command object is a specific command that is used to

manipulate data in a data source in a connected

environment.

A Command object represents a DML statement or a stored

procedure that is used to retrieve, insert, delete, or modify

data in a data source.

The two types of operations performed by a command

object to retrieve and modify data in a data source are:

Synchronous operations

Asynchronous operations

Let us discuss these operations in detail.

Working with Command Objects

Inform the students that in this session, the focus will be on learning about the connected

environment. Explain to the students that in a connected environment, since users have tobe continuously connected to a data source to retrieve the data, various command objects

are used that provides data to the application in a read-only and forward-only mode.

Explain command objects, and list the two types of operations performed by a command

object to retrieve and modify data in a data source, synchronous and asynchronousoperations.


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Slide 6



Session4

During synchronous operations, the command objects are

linked to each other.

Executing command objects synchronously results in a

sequential execution, where each database command must

complete before the next command is executed.

Synchronous operations are performed with the help of the

following command objects:

DbCommand object

DbParameters object

DbDataReader object

Working with Command Objects (Contd.)

Executes a command in a data source

against a valid open connection

Assigns parameterized values to stored

procedures

Retrieves a forward-only, read-only data

from the data source

Explain how command objects are executed synchronously with the help of an examplegiven in the SG. Use this animated slide to explain the various command objects that are

used to perform synchronous operations.

Discuss the code given in the SG. Explain that the ExecuteNonQuery() method returns

-1 when a SELECT statement is executed. On the other hand, if an INSERT, DELETE, or

UPDATE statement is executed, this method returns the number of rows affected.


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Slide 7



Session 4

Which method of the DbCommand object executes a DML

statement against a connection and returns the number of

rows affected?

1. ExecuteReader()

2. CreateObjRef()

3. ExecureNonQuery()

4. ExecuteScalar()

Just a minute

Answer:

3. ExecuteNonQuery()

The objective of this JAM is to revise the concepts related to command objects covered inthe preceding slides.

Slide 8



Session 4

Asynchronous execution of commands enhances the overall

performance and responsiveness of the client application.

ADO.NET supports asynchronous execution of commands

to enable parallelism by allowing the client application to

execute commands while waiting for the response from a

previously issued command.

The asynchronous execution of commands is carried out inthe SQLCommand class.


Move the discussion to explain how command objects are executed asynchronously.


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Slide 9



Session4

The SQLCommand class provides the following methods for

asynchronous execution of commands:

BeginExecuteNonQuery()

BeginExecuteReader()

BeginExecuteXmlReader()


Starts the process of asynchronously

executing a Transact-SQL statement or

stored procedure that does not return

rows

Starts the process of asynchronously

executing a Transact-SQL statement or

stored procedure that returns rows

Initiates the asynchronous execution of

the Transact-SQL statement or stored

procedure that is described by theSqlCommand and returns the result as

an XMLReader object

Use this slide and the next slide to explain the various methods, provided in the

SqlCommand class, to execute command objects asynchronously.

Slide 10



Session4

EndExecuteNonQuery()

EndExecuteReader()

EndExecuteXmlReader()


Completes the asynchronous execution

of a Transact-SQL statement or stored

procedure


of a Transact-SQL statement or a stored

procedure, thereby, returning therequested SqlDataReader


of a Transact-SQL statement or a stored

procedure, thereby, returning XML data


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Slide 11



Session 4

Another way of retrieving data asynchronously is by using

Multiple Active Result Sets (MARS).

MARS allows the execution of multiple data readers on a

single connection.

By default, MARS feature is disabled in an application. You

can enable MARS in the connection string, as shown in the

following code snippet:

String connectionString = "Data

Source=SQLSERVER01;Initial

Catalog=AdventureWorks;User

id=sa;Password=niit#1234;

MultipleActiveResultSets=True";


Enabling MARS property

to True

Link this topic with asynchronous operations by telling the students that another way ofretrieving data asynchronously is by using Multiple Active Result Sets (MARS).

Explain MARS with the help of examples provided in the SG. Describe to the students

how MARS is enabled in a Windows application.

Slide 12



Session 4

What is the function of the EndExecuteReader()

method of the SqlCommand class?

1. Asynchronously executes a stored procedure that returns

rows

2. Executes the stored procedure and returns the result as anXmlReader object

3. Asynchronously executes a stored procedure that does not

return rows

4. Executes the stored procedure and returns the result as anSqlDataReader object

Just a minute

Answer:

4. Executes the stored procedure and returns the result as anSqlDataReader object


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The objective of this JAM is to revise the concepts related to asynchronous operationscovered in the preceding slides.

Slide 13



Session4

A data adapter is integral to the working of ADO.NET

because data is transferred to and from a database through

a data adapter.

A data adapter retrieves data from a database into a

dataset.

The data adapter first compares the data in the dataset with

that in the database and then updates the database.

Data from a database can be accessed by configuring a

data adapter.

Working with Data Adapters

Before starting with this session, conduct a brief recap by asking students the following

questions:

What is a dataset?

What are dataviews?

Initiate a discussion in the class on data adapters. Explain data adapters and their role in a

connected environment.


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Slide 14



Session 4

Following are the data adapters that can be configured to

connect to a database:

SqlDataAdapter

OleDbDataAdapter

OdbcDataAdapter

OracleDataAdapter

Working with Data Adapters (Contd.)

Accesses data specifically from Microsoft

SQL Server

Accesses data from a database that is

supported by an OLE DB data provider


supported by an ODBC data provider


supported by an Oracle data provider

Use the animated slide to list the various dataadpaters that can be configured to connect toa database in Visual Studio .NET.

Slide 15



Session 4

The following properties and methods of a data adapter can

be used to perform various operations on a database:

SelectCommand

InsertCommand

UpdateCommand

DeleteCommand

Fill()

Update()


Refers to a DML statement or a stored procedure

to retrieve data from a database

Refers to a data command to insert data into a

database

Refers to a data command to update a database

Refers to a data command to delete data from a

database

Fills the dataset with the records from a database

Executes the corresponding Insert, Update, or

Delete commands for each inserted, modified,

or deleted row to reflect the changes in a

database

Use the animated slide to explain the properties and methods of a data adapter for

performing various operations on a database.


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Slide 16



Session 4

Consider the following code snippet of creating aDataAdapter object and using the SelectCommand

property of the object:

SqlConnection cn = new

SqlConnection();

cn.ConnectionString = "Data

source=SQLSERVER01;Initial

catalog=HR;User id=sa;

Password=niit#1234";

DataSet DataSet1 = new DataSet();

SqlDataAdapter da = new

SqlDataAdapter();

SqlCommand cmd=new SqlCommand

("Select * from Employees", cn);

da.SelectCommand = cmd;

da.Fill(DataSet1);


Set a connection string

Creating a DataSet object

Creating a SqlDataAdapter

object

Passing the SQL query to thecommand object

Retrieving records from theEmployees tableFilling the dataset with records

from the Employees table

Use the animated slide to explain a code snippet of creating and using a data adapter

object. You can also use the code snippet given in the SG for updating and saving the data

modifications in a datatable.

Slide 17



Session4

A data adapter handles data transfer between the database

and the dataset through its properties and methods, and

displays data through the process of table mapping.

After a dataset has been created, the data adapter uses the

process of table mapping to map the columns in the

database table with the dataset columns.

A data adapter uses the TableMappings property, a

collection ofDatatableMapping objects that is used for

mapping between the database table and the DataTable

object in the dataset.


Lead the discussion towards the TableMapping property of data adapters. Explain the

process of table mapping, which is the process of data transfer between the database and

the dataset through its properties and methods.


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Slide 18



Session 4

A major challenge related to data access is that more than

one user might need to simultaneously access data in a

database.

Another challenge is more than one user might need to

access the data anytime, anywhere. This challenge can be

overcome by implementing database locking while a

transaction is executing.

However, if database locking is not implemented, it can lead

to data concurrency conflicts that arise from multiple

updates being performed on the database.


Inform the students that after making the changes in the datatable through a data adapter,

you need to ensure that the changes are committed and updated in the datatable.

Otherwise, it leads to data concurrency conflicts. Initiate a discussion in the class on how

persisting changes to a data source can create several challenges. Explain these challenges

with the help of the example given in the SG.

Slide 19



Session 4

Resolving data concurrency conflicts is a business decision,

with the following choices:

Prioritized on time; first update wins

Prioritized on time; last update wins

Prioritized on role

Prioritized on location

User resolves the conflict


Lead the discussion to explain how data conflicts in a data source can be resolved.


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Slide 20



Session4

A significant way to increase the performance of data

updates is to update and send the changes to the database

in batches. This is known as batch updates.

Batch updates are performed by using theUpdateBatchSize property of the SqlDataAdapter

object.

By default, the UpdateBatchSize property is set to 1.

One way to confirm that the changes are being sent to thedatabase server in batches is to add a RowUpdated event

to the SqlDataAdapter object. This event will show the

number of rows affected in the last batch.


Inform the students that a significant way to increase the performance of data updates is to

update and send the changes to the database in batches. Explain batch updates with the

help of the code given in the SG.

Slide 21



Session4

ADO.NET provides support for classes that can create any

provider-specific objects. These classes are known as theDbProviderFactories classes.

The DbProviderFactories class contains a method

called GetFactoryClasses that returns a data table,

which is populated with data from various providers, as

shown in the following figure.


Move the discussion towards factory classes. Tell the students that this is a new feature of

ADO.NET. Explain the use of factory classes with the help of the example given in the

SG.


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Slide 22



Session 4

_______ class can create any data provider-specific object.

1. DbCommand

2. DbProviderFactories

3. DbParameter

4. DbConnection

Just a minute

Answer:

2. DbProviderFactories

The objective of this JAM is to revise the concepts related to data adapters covered in the

preceding slides.

Slide 23



Session 4

Problem Statement:

The HR Manager of Tebisco needs to update the number of

vacancies, for those positions where the number of vacanciesis not more than 10. This updation will be based on the current

position code of employees.

As a part of the development team, you need to execute two

queries, one to retrieve the number of vacancies per position

code, and the other to update the number of vacancies on thebasis of the current position code of employees.

You need to develop an application that can execute bothqueries on a single database connection.

Hint: You need to access the InternalJobPosting and

Employee tables of the HR database.

Demo: Manipulating Data in a Connected Environment

The objective of this activity is to see the advantage of MARS.

Use this slide to conduct the activity.


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You can access the solution of this activity from the following path in the TIRM CD:

Datafiles_For_Faculty\ADO.NET\Chapter 01\Activity1.

Slide 24



Session4

In this session, you learned that:

A connected environment is one in which a user or an

application is constantly connected to a data source.

A disconnected environment is one in which a user or an

application is not directly connected to a data source.

The two types of operations performed by a command object

to retrieve and modify data in a data source are:Synchronous operations

Asynchronous operations

During synchronous operations, the command objects arelinked to each other.

Synchronous operations are performed with the help of the

following command objects:

DbCommand object

DbParameters object

DbDataReader object

Summary

Use this slide and the following slides to summarize the key points of the session.

Slide 25



Session4

ADO.NET supports asynchronous execution of commands to

enable parallelism by allowing the client application to executecommands while waiting for the response from a previously

issued command.

The SqlCommand class provides the following methods for

asynchronous operations:

BeginExecuteNonQuery()

BeginExecuteReader()

BeginExecuteXmlReader()

EndExecuteNonQuery()

EndExecuteReader()

EndExecuteXmlReader()

MARS allows the execution of multiple data readers on a

single connection.

Summary (Contd.)


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Slide 26



Session 4

A data adapter, which is a part of the connected environment,

retrieves data from a database into a dataset.

The data adapters that can be configured to connect to a

database in Visual Studio .NET are:

SqlDataAdapter

OleDbDataAdapter

OdbcDataAdapter

OracleDataAdapter

Summary (Contd.)

Slide 27



Session 4

The following properties and methods of a data adapter can be

used to perform the various operations on a database:

SelectCommand

InsertCommand

UpdateCommand

DeleteCommand

Fill()

Update()

A data adapter handles data transfer between the database

and the dataset through its properties and methods, and

displays the data through the process of table mapping.

Summary (Contd.)


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Slide 28



Session 4

Resolving data concurrency conflicts is a business decision,

with the following choices:

Prioritized on time; first update wins

Prioritized on time; last update wins

Prioritized on role

Prioritized on location

User resolves the conflict

A significant way to increase the performance of data updatesis to update and send the changes to the database in batches.

This is known as batch updates.

ADO.NET provides support for classes that can create any

provider-specific objects, such as SqlClient, Odbc,

OracleClient, and OleDb. These classes are known asDbProviderFactories classes.

Summary (Contd.)

The following questions can be asked by the student in this session:

1. What is the advantage ofStringBuilder overString?Ans. While assigning a value to a string object, a new object is created with every

assignment. There is a slight overhead when this is done repeatedly.

The StringBuilder class provides an efficient way to repeatedly add bits on to a string.

You provide a string with an initial capacity and can add more bits of strings to it without

the overhead of creating a new object.

The performance difference will be too small to measure if you are only doing

a few concatenations. However, if you are performing operations in a loop, such asbuilding the HTML code for a web page, then StringBuilder has a definite advantage.

2. What rule is followed while deciding the settings of the batch size whenusing SqlBulkCopy?

Ans. Increasing the batch size can improve performance of the application. However,

constructing the batch on the client and handling the results on the server also creates

overheads. Therefore, you should not set the batch size to zero (one batch).

FAQs


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Usually batch size between 100 and 1000 rows can generate good performance result.However, you have to perform tests to derive the optimal batch size for a scenario.

3. What is DDL?Ans. Data Definition Language (DDL) is a language used by a database management

system that allows the users to define the database, specify data types, structures, andconstraints on the data. For example, CREATE TABLE, CREATE INDEX, ALTER, andDROP are DDL statements.

4. When is the InvalidOperationException raised?Ans. This exception is thrown when a method call is invalid for the object's current state.

5. What is the advantage of asynchronous operations?Ans. Some database operations, such as command executions, can take significant time tocomplete. In such a case, single-threaded applications must block other operations and

wait for the command to finish before they can continue their own operations. In contrast,

being able to assign the long-running operation to a background thread allows the

foreground thread to remain active throughout the operation. In a Windows application,

for example, delegating the long-running operation to a background thread allows the user

interface thread to remain responsive while the operation is executing.

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09 Ddcauado.net Cg Session04